1. Field Of The Invention
The present invention relates to a modified or "humanized" bovine milk product that approximates the composition of human milk protein, which can be used in infant formulas. The present invention also relates to a method for its production that can be readily adopted by the dairy industry in the manufacture of the product.
2. Description Of The Art
Milk is one of the most nutritionally complete foods, a fact reflected in it's widespread use as a dietary supplement in many parts of the world. This quality is of utmost importance during the neonatal period in mammals when it is the only or primary nutrient source. The nutrient content of milk show considerable variation among species with respect to the individual components and appears to be related to the rate of growth of the offspring.
Breast feeding is generally recognized as the preferred method of feeding human infants, however, when for a variety of reasons mother's milk is unavailable, infant formulas based on cow's milk are used. The use of modified or "humanized" bovine milk in infant formulas designed to simulate human milk as a substitute or supplement, has long been a subject of continuing research.
The composition of bovine milk and human breast milk differ significantly with respect to total protein concentration, the nature of individual proteins and acid coagulability. These compositional differences provide the basis for enhanced nutritive and digestive qualities attributed to human milk so important in infant nutrition. Bovine milk contains about 3.5 g protein/100 mL, whereas, human milk averages about 1.2 g/100 mL. While the protein level of bovine milk can be readily reduced to that of human milk, the casein, whey and nonprotein nitrogen (NPN) differ significantly. The relative contents of casein, whey and NPN are 78%, 17% and 5% respectively for bovine milk, versus 35%, 40% and 25%, respectively, for human milk. The casein/whey protein ratios of human milk and cow's milk are 0.4-0.7 and 3.0-4.7 respectively. Furthermore, the individual components comprising the casein and whey fractions of human milk and cow's milk are quite different. In human milk the casein fraction consists of only .beta.-casein and the whey consists of .alpha.-lactalbumin and other minor whey components; lactoferrin, immunoglobulins, serum albumin, and lysozyme but is devoid of any .beta.-lactoglobulin. In bovine milk the major casein component is .alpha..sub.s1 -casein and contains .beta.-lactoglobulin in the whey fraction. Modification of bovine milk or its fractions to simulate human milk protein composition must of necessity be concerned with the removal of .beta.-lactoglobulin and with an enrichment of .beta.-casein either by supplementation with .beta.-casein or by the elimination of the .alpha..sub.s -caseins.
A variety of methods including precipitation of selected bovine milk components and enzymic modifications have been utilized with varying degrees of success in efforts to "humanize" bovine milk. See Li-Chan E. et al. Can. Inst. Food Sci. Technol. J. 21:200 (1988). Methods such as dilution, heating, calcium reduction and homogenization of bovine milk have not been successful in simulating the clot of human milk formed under physiological conditions of the infant stomach, but a mild rennin treatment resulting in selective precipitation of part of the protein after heating has been successful in producing a modified bovine milk with coagulability characteristics similar to that of human milk.
Efforts directed to the elimination of .beta.-lactoglobulin consist of gel filtration of whey (Forsum, E. J. Dairy Sci. 57:665 (1974); Mathur B. et al., J. Diary Sci. 62:99 (1979)), selective precipitation from ultrafiltered and demineralized whey (Amundson C. J. Food Proc. Preserv. 6:55 (1982)) and by precipitation with ferric chloride (Kuwata T. et al., J. Food Sci. 50:605 (1985)) or polyphosphate (Al-Mashikhi S. et al. J. Food Sci. 52:1237 (1987)). .beta.-Casein enriched preparations have been obtained by rennin modification of bovine casein (Li-Chan, supra). Although these methods are capable of effecting selected changes in milk composition, they are generally batch procedures and are not especially conducive to plant operations when projected to a commercial scale.
It has been previously reported that microfiltration of 1 bovine skim milk using membranes with porosities of 0.1 or 0.2 micrometers (.mu.M) at room temperature effected a fractionation of the whey and casein proteins and a micellar size separation (Woychik J. et al. Abstracts IFT Annual Meeting #81 (1990)). The permeates obtained had casein/whey ratios of 0.7-0.9 which are comparable to that of human milk. The casein component distribution of the permeates, however, was not significantly different from normal bovine casein.
U.S. Pat. No. 4,925,680 discloses a process for the production of liquid and powdered bifidogenic infant and dietetic foods in which mammals' milk, in particular cows' milk, is treated with neuraminidase to cleave the sialic acid in the milk. By splitting off sialic acid, the bifidogenic oligosaccharides of the residual protein will be accessible as growth factors for the bifidus bacteria which dominates the intestinal flora of breast-fed infants. The production of bifidogenic factors in cows' milk is suggested as a means of adapting cows' milk to more closely resemble human milk. U.S. Pat. No. 4,963,384 also discloses a method of producing bifidogenic factors in cows' milk but uses acid hydrolysis as the means for achieving the bifidogenic product.
U.S. Pat. No. 4,944,944 discloses a method for fortifying cow's milk with salt-activated lipase (BAL) to be used as an infant formula. The lipase, present in human milk but not cow's milk, is added to improve the absorption or digestion of ingested fats. The presence of BAL is human milk as stated in the patent, is a compensatory mechanism for the infant's immature pancreatic function.
U.S. Pat. No. 4,954,361 discloses a hypoallergenic milk which has the flavor and smell of natural whole mammalian milk. The hypoallergenic milk is preferably made from the ultrafiltrated permeate of cow's milk, which is substantially free of milk protein and fat. The permeate is then supplemented with, among other things, hypoallergenic protein and fat. The milk is intended for use by children and adults allergic to cow's milk.
German Specification 3,743,440 (Offenlegungschrift) discloses the separation of milk into soluble and insoluble components with microporous membranes using tangential flow. However the process does not disclose any pretreatment of the milk or the collection of the permeate for use in infant formulas.
The dairy industry currently utilizes ultrafiltration with membranes having 10,000 molecular weight cut-offs for the concentration of milk prior to cheese making and for the concentration of cheese whey. These operations do not yield a permeate product containing protein as the pores in the membrane used do not allow the passage of the protein.